Issue Resolved: https://github.com/puikinsh/Adminator-admin-dashboard/issues/107
When you want to run PHP on same page as of the content then your page should be having extension of '.php' instead of '.html'. I have changed the page name to .php and add the php content for post there itself as asked.
Now POST method is working and also displaying the data below the form. You can although show the data wherever you want.